The present invention concerns replaceable ink supply containers for providing ink to a high flow rate ink delivery system.
High throughput printing systems, such as those used in high speed printers and color copiers, or large format devices put heavy demand on an ink delivery system. The printhead must operate at a very high frequency. At the same time, print quality expectations keep rising. In order to maintain high print quality, the printhead must be able to rapidly eject ink without causing large fluctuations in the printhead pressure level.
One approach to this is to provide a pressure regulator integral to the printhead. The regulator receives ink at a first pressure and delivers ink to the printhead at a controlled second pressure. In order for this control to work, the first pressure must always be greater than the second pressure. Because of dynamic pressure drops, very high pixel rate printing requires that the first pressure be at a positive gauge pressure.
One example of an ink cartridge that can be pressurized is described in U.S. Pat. No. 4,568,954. Other references include U.S. Pat. Nos. 4,558,326; 4,604,633; 4,714,937; 4,977,413; Saito U.S. Pat. Nos. 4,422,084; and 4,342,041.
One problem with previous high throughput devices is predicting when the consumable will be exhausted. It is important that the system stop printing when the ink cartridge is nearly empty, with a small amount of stranded ink. Otherwise, dry firing and consequent printhead damage may occur. Printheads for such high throughput devices tend to be expensive. What is needed is an ink cartridge that offers pressurized ink and provides an accurate means of indicating low ink.
Various ways have been developed for detecting the amount of ink in an ink container. However, this problem becomes very difficult when the ink is to be pressurized. In such a case, the ink must be held in a pressure vessel.
U.S. Pat. No. 4,568,954 employs electrodes that measure a resistance path through the ink. A problem with this approach is that it is dependent upon electrical properties of the ink. What is needed is a way of sensing the volume of the ink in a collapsible bag reservoir that is surrounded by a pressure vessel. Further, what is needed is a way of accessing the sensing signal without negatively impacting the integrity of the construction.
This invention is an ink container for use in an off-carriage printing system. The ink container contains a collapsible reservoir filled with ink that is fluidically connectable to a conduit that leads to a pressure regulator. The outlet of the regulator delivers ink to a printhead. A pressure vessel surrounds the bag. The system pressurizes the pressure vessel, which results in pressurized ink being delivered to the regulator.
The ink container has a sensor that infers the actual volume of ink in the reservoir by sensing the relative position of the reservoir walls. This sensor is mounted between the pressure vessel and the collapsible reservoir.
The sensor is electrically connected to pads that are accessible from the outside of the ink container. Leads route from the pads, through a seal zone, and to the sensor. The seal is provided by a compressed o-ring.
In accordance with another aspect of the invention, a method of assembling an ink container to be installed in an inkjet printing system is described, the inkjet printing system having a printhead for ejecting ink on media. The method comprises the steps of:
(a) providing a first housing member including a fluid pathway with a fluid outlet for providing ink to said printhead;
(b) fluidically coupling a collapsible reservoir to said fluid outlet;
(c) attaching an ink level sensing circuit to said collapsible reservoir;
(d) attaching a plurality of container contacts on an outside surface of said first housing member;
(e) routing a plurality of electrical paths that couple said sensing circuit to said container contacts;
(f) attaching a second housing member to said first housing member, said second housing member abutting said first housing member along a seal zone, said first and second housing members forming a pressure vessel that surrounds said collapsible reservoir, said pressure vessel and said collapsible reservoir defining a pressurized region therebetween, said plurality of electrical paths passing through said seal from said pressurized region to said outside atmosphere.